Rosuvastatin is generic name for (+)-7-[4-(4-fluorophenyl)-6-isopropyl-2-(N-methyl-N-methylsulfonylamino)pyrimidin-5-yl]-(3R,5S)-dihydroxy-(E)-heptenoic acid administered in the therapy as its calcium salt as commercial drug, and illustrated in Formula 1 hereinafter, which compound is an inhibitor of the enzyme 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMG CoA reductase), useful in the treatment of hyperlipidemia, hypercholesterolemia and atherosclerosis. Rosuvastatin and the synthesis of rosuvastatin calcium was first described in patent EP-B-521 471; in the last two steps of the whole synthesis provided by hydrolysis of methyl ester of rosuvastatin (methyl rosuvastatin) in polar solvent, e.g. ethanol, in the presence of a base, e.g. sodium hydroxide, following by isolation of sodium salt of rosuvastatin and converting said sodium salt of rosuvastatin with a water soluble calcium salt under aqueous conditions to calcium salt of rosuvastatin. The process for the preparation of the intermediates described in EP-B-521 471 patent is incorporate herein by reference.
WO 2005/023778 describes a process for the preparation of rosuvastatin calcium by conversion of C1 to C4 alkyl ester of rosuvastatin, preferably tert-butyl ester of rosuvastatin with a base, preferably sodium hydroxide, in the presence of a C1 to C4 alcohol, preferably ethanol, to a solution of rosuvastatin salt, e.g. its sodium salt and converted said salt into rosuvastatin calcium by adding a source of calcium to said solution.
A novel crystalline form of rosuvastatin calcium can be prepared by crystallization of amorphous form of rosuvastatin calcium from a mixture of: (i) water and acetonitrile in the ratio of 1:1 by volume; (ii) water and acetone in the ratio of 1:1 by volume; or water, methanol and methyl tert-butyl ether in the ratio of 1:1:1 by volume, what is described in WO 2000/042024.
WO 01/60804 discloses certain novel amine salt with rosuvastatin, which may be prepared by addition of an appropriate amine or base to a solution of rosuvastatin acid in acetonitrile or ethyl acetate. Certain novel amine salts of rosuvastatin, preferably its crystalline methylammonium salt, may be used in the preparation of amorphous calcium salt of rosuvastatin, which process comprises sequential reaction of the crystalline methylammonium salt of rosuvastatin with sodium hydroxide, followed by a water soluble calcium salt, such as calcium chloride, under aqueous conditions. An approach is disclosed in WO 2005/051921 where rosuvastatin calcium salt is purified by conversion into isopropylammonium or cyclohexylammonium salt and back to calcium salt.

It is well known that alkali metal salts of organic acids are often hygroscopic what may cause problems at isolation. Indeed the isolation of sodium salt of rosuvastatin, which can be an intermediate in preparing rosuvastatin calcium salt, might be unrepeatable in yield and physical state what depends on the reaction conditions and evaporation of solvents, which is difficult to control. International publication WO 2005/23778 tried to avoid said problems without isolating rosuvastatin sodium salt by extraction of impurities from its aqueous solution into water immiscible solvent, but by using C1 to C4 alcohols as reaction medium a risk of conversion into specific impurities still existed. Namely, it is known that β-hydroxy acids in alcoholic alkali solution are submitted to dehydration what may lead after realkoxylation into special side products (see FIG. 1, Scheme 1, wherein R and R1 independently denotes C1 to C5 alkyl group), O-alkyl derivatives of rosuvastatin, e.g. O-ethyl rosuvastatin.
Therefore a need for an efficient process for preparing pure amorphous rosuvastatin calcium, without any significant amounts of side products and in having the exact stoichimetric content without other alkali metal cation, still exists.